Herbicides generally can be classified into two broad categories based on the time at which it is applied: pre-emergent herbicides and post-emergent herbicides. Pre-emergent herbicides act by preventing emergence of seedlings and therefore are useful for preventing new weed growth from developing. Post-emergent herbicides, on the other hand, are effective at eradicating fully developed weeds. Given the different mechanisms of action and the developmental stages of the weeds in which they act, one would not expect pre-emergent and post-emergent herbicides to have any effect on one another. Therefore, it was surprising to discover that certain mixtures of pre-emergent and post-emergent herbicides synergistically enhance the pre-emergent and post-emergent herbicidal effects of one another, i.e. the activities of the mixtures are greater than the sum of the individual activities. Thus, an unforeseeable synergistic effect is present, and not just an addition of activities.